Delayed action switching device



968 P. F. GANDOLFO ETAL 3,416,109

DELAYED ACTION SWITCHING DEVICE F iled Dec. 8, 1965 4 SheetsSheet 1 Iwmibm:

@AW M/TM Dec. 10, 1968 P. F. GANDOLFO ETAL 3,416,109

DELAYED ACTION SWITCHING DEVICE 4 Sheets-Sheet 2 Filed D60. 8, 1965 4 Sheets-Sheet 5 1968 P. F. GANDOLFO ETAL DELAYED ACTION SWITCHING DEVICE Filed Dec. 5, 1965 United States Patent 3,416,109 DELAYED ACTION SWITCHING DEVICE Peter F. Gandolfo, Wellesley, and Gerald F. Rnsses,

Watertown, Mass., asisgnors to Lewis Shepard Company, Watertown, Mass., a corporation of Massachusetts Filed Dec. 8, 1965, Ser. No. 512,487 3 Claims. (Cl. 335-59) ABSTRACT OF THE DISCLOSURE This invention relates generally to material handling equipment and more particularly to a delayed action switching device for use with a lift truck having a vertically adjustable platform for raising the operator to the level of the goods to be handled.

In apparatus of the above-mentioned type, the platform is usually raised and lowered on a vertical mast assembly by means of a powered elevating mechanism carried on the truck chassis. The elevating mechanism is normally connected to the platform by means of one or more lifting chains or the like which extend over sheaves on the mast assembly. Under normal operating conditions, the lifting chains remain in tension as they support the platform at various levels on the mast assembly. However, experience has indicated that at times, due to faulty judgment on the part of the operator, the platform may become engaged on an adjacent shelf or other fixed member. Should this occur without the operators immediate knowledge when the platform is descending, con tinued operation of the elevating mechanism will cause slack to develop in the lifting chains. Creation of excessive slack will in turn result in the chains jumping their respective sheaves, thus rendering the lifting mechanism inoperable. When this occurs, the operator may be left stranded on the elevated platform without means for reactivating the lifting mechanism. Moreover, should the platform subsequently become disengaged, it Will fall until brought to a sudden stop by tension again being developed in the lifting chains. This abrupt fall may cause the operator to lose his balance and fall from the platform.

In an effort to overcome the above difiiculties, it has heretofore been proposed to provide a switch in the truck control circuit connected in series with the main power supply. The switch opens automatically upon the development of any slack in the lifting chains. Although this arrangement will succeed in avoiding the development of excessive slack in the lifting chains, experience has indicated that it is too sensitive for practical operation. To explain, an alert operator will usually notice when the platform becomes engaged on a fixed object in time to stop the elevating mechanism and prior to the development of excessive slack in the lifting chains. Although a slight amount of slack has in fact developed at this point, the lifting chains are still on their respective sheaves and the lifting mechanism remains operable. Thus, the operator may immediately elevate the platform to free it from its engaged position. However, with a switch of the above-mentioned type, the development of even a slight amount of slack will immediately open the switch and cut out the power supply. Until the switch is manually reset to the closed position, further operation of the lifting mechanism is herefore not possible. Thus it can be seen that the above arrangement is overly sensitive and impractical.

The above difiiculties have now been successfully overcome by the present invention, an object of which is to provide an improved switch which will remain closed until slack develops in the lifting chains in excess of that occurringduring normal operation of the apparatus by an alert operator, yet less than that which will cause the lifting chains to jump their respective sheaves and render the lifting mechanism inoperable. In this manner, an alert operator who immediately senses that the platform has become engaged on a fixed object, can reverse the operation of the lifting mechanism to raise the platform without having the power source interrupted by an overly sensitive switch. However, should excessive slack develop, the switch will open automatically to prevent the lifting chains from jumping their respective sheaves.

Another object of the present invention is to provide a delayed action switch for use with a material handling truck of the type having a vertically adjustable platform on which the operator rides during the operation of the truck, the said switch being operable to interrupt the main power supply of the truck only upon the attainment of a dangerous amount of slack in the lifting chains.

A still further object of the present invention is to provide a delayed act-ion switch which will remain closed during the development of a slight amount of slack in the lifting chains, but which will open when the slack approaches the level at which the lifting chains may be in danger of jumping their respective sheaves.

These and other objects of the present invention will become more apparent as the description proceeds with the aid of the accompanying drawings in which:

FIG. 1 is a perspective view showing a fork lift truck embodying the concepts of the present invention;

FIG. 2 is a schematic perspective illustration of the means utilized to connect the delayed action switch of the present invention to the vertically adjustable platform on the fork lift truck shown in FIG. 1;

FIG. 3 is a horizontal sectional view of a switch according to the present invention taken along line 3-3 of FIG. 4;

FIG. 4 is a sectional view in elevation taken along line 44 of FIG. 3 showing the switch held in its closed position 'by tension developed in the lifting chains;

FIG. 5 is a sectional view similar to FIG. 4 illustrating the reaction of the switch to a slight yet tolerable amount of slack in the lifting chains;

FIG. 6 is a sectional view similar to FIGS. 4 and 5 showing the switch after it has been opened by the development of a dangerous amount of slack in the lifting chains; and,

FIG. 7 is a rear view of the mast assembly showing the operating platform elevated thereon.

Referring initially to FIGS. 1 and 2 wherein are best shown general features of the invention, a material handling truck 10 is shown comprising a mobile chassis 12 having load bearing wheels 14 at its forward end and a steerable traction wheel 16 at its rear end beneath housing 18. Wheel 16 is driven by a conventional electric drive (not shown) in housing 18, the drive in turn being pow ered by a rechargeable storage battery 20. The truck is further provided with an upstanding extensible mast assembly generally indicated at 22 which as can best be seen in FIG. 7, is comprised in part of fixed outer support members 24 extending upwardly in spaced parallel relationship from the truck chassis 12. A second pair of spaced inner support members 26, herein shown as I- beams interconnected at their lower ends by cross memher 28 and at their upper ends by plate 30, form the extensible portion of the mast assembly located between fixed support members 24. Upper and lower pairs of guide wheels 32 and 34 on outer support members 24 engage the outboard flanges of inner support members 26 to thus provide rolling engagement therebetween during extension of the mast assembly. A hydraulic cylinder 36 is mounted on chassis 12 in an upstanding vertical position between inner support members 26. Cylinder 36 is provided with an extensible piston rod 38 which terminates at its upper end in a substantally horizontal shoe 40 having brackets 42 depending downwardly therefrom. The brackets provide a means of supporting a horizontally disposed shaft 44 on which is rotatably mounted chain sheaves 46 and pulleys 48 As can best be seen in FIGS. 1 and 2, a horizontal base 50 together with a control panel 52 extending upwardly from the rear edge thereof form a carriage assembly 53 located on the forward end of truck 10. The carriage assembly is movably mounted on the mast assembly 22 by means of four guide rollers 54 engaging the inboard flanges of inner support members 26. Lifting chains 56 are connected at one end to chassis 12 by means of chain anchors 58. The chains pass over chain sheaves 46 on shaft 44 and are connected at their other ends to the base 50 of carriage asesmbly 53 as at 60 (see FIG. 2).

With this arrangement, it can therefore be seen that by forcing hydraulic fluid into cylinder 36, piston rod 38 will be vertically extended, thus carrying the chain sheaves 46 with it. Since the lifting chains 56 Which pass over the chain sheaves are fixed at one end by means of a chain anchor 58 to the truck chassis 12 and at the other end to the base 50, vertical displacement of the carriage assembly 53 on the inner support members 26 f mast assembly 22 results. As the piston rod continues to rise, shoe 40 will eventually contact plate 30, thus causing the inner support members 26 to begin rising between the stationary outer support members 24. By telescopically extending the inner support members 26 between outer support members 24, the height to which the carriage assembly 53 may be raised is increased, thus providing the truck with a higher lift capacity.

Although not illustrated in the drawings, it should be understood that the flow of hydraulic fluid to cylinder 36 is controlled by a conventional pump and electric motor powered by storage battery 20. As shown in FIG. 1, a power control assembly generally indicated at 62 together with a steering wheel 64 provide the means for enabling an operator standing on base 50 to fully control the complete operation of the truck. Steering wheel 64 is connected to traction wheel 16 by means of steering cables 66 which extend over pulleys 48 on shaft 44 before proceeding downwardly to pass around lower pulleys 68 supported on the chassis 12 by means of upstanding brackets 70. By the same token, the power control assembly 62 is electrically connected to the various drive components and electric pumps mentioned above by means of a control cable 72 which also extends over one of the pulleys 48.

As can best be seen in FIG. 1, base 50 is further provided with parallel lifting forks 74 extending outwardly from the forward edge thereof. These lifting forks may be inserted beneath articles to be lifted by first elevating carriage assembly 53 to the desired level and then advancing the truck until the forks are suitably inserted.

As previously mentioned, when operating a lift truck of the above-mentioned type, there is a danger of inadvertently engaging the lift forks 74 on a fixed member such as the edge of a storage bin or shelf. If the forks remains engaged on the shelf while the carriage assembly 53 is being lowered, slack will immediately begin to develop in the lifting chains 56 and steering cables 66 due to the continued descent of piston rod 38 carrying sheaves 46 and pulleys 48. If the operator is alert, he will immediately reverse the travel of piston rod 38 prior to the development of excessive slack, thus causing the forks to be lifted from their engaged positon on the adjacent shelf. However, if the operator is not alert, or if his attention is distracted by surrounding conditions, he may not react in time to stop the descent of piston rod 38 before excessive slack develops. This may in turn cause the various chains 56 and cables 66 to jump their respective sheaves and pulleys, thus rendering the truck controls inoperative.

To avoid this danger, the present invention contemplates use of a delayed action switch 75 of the type illustrated in detail in FIGS. 3-6. This switch, 'which is the essence of the present invention, is comprised basically of a housing 76 including an internal shelf 78 on which is supported a pair of spaced electrical contacts 80. Each contact 80 is formed by the head of a bolt 82 which extends downwardly through a hole in shelf 78. The bolt 82 is electrically insulated from shelf 78 by means of an insulating bushing 84 (see FIG. 4) and two insulating washers 86. Each bolt 82 is held in place by a nut 88 against which the leads 90 from the electrical control circuit of the truck are clamped by means of a second nut 92 also threaded onto bolt 82. It can therefore be seen that by connecting the switch in the electrical control circuit of the truck in series with the main power source (storage battery 20), the circuit will remain open and inoperable until the gap between the spaced electrically insulated contacts 80 is bridged by an electrically conductive material.

A substantially rectangular plate 94 overlies shelf 78 and is pivotally mounted to the housing by means of a shaft 96 welded along one edge thereof, which shaft is seated between spaced support brackets 100 on the housing wall. A second electrically conductive somewhat diamond-shaped plate 102 having a pair of downwardly protruding contacts 104 is attached to plate 94 by means of two screws 106. Each of the screws 106 is also electrically insulated from plate 94 (see FIG. 4) by means of an insulating bushing 108 and washers 110. It can therefore be seen that the interconnected plates 102 and 94 form an armature assembly generally designated by the reference numeral 112, which assembly is supported for pivotal movement about the longitudinal axis of shaft 96. When the armature assembly is in the position shown in FIG. 4, the gap between spaced electrically insulated contacts 80 is bridged by electrically conductive plate 102 in contact therewith through depending contacts 84.

The armature assembly 112 is normally held in the closed position shown in FIG. 4 by means for a permanent magnet 114 fixed to the side of shelf 78 by means of screws 116. The attractive force of magnet 114 acts on plate 94 to draw the armature assembly downwardly, thus bringing the opposed sets of contacts 80 and 104 together.

The switch is further provided with an operating plunger 118 extending downwardly through a bushing 120 in housing 76 and past two spaced prongs 122 on plate 94. An enlarged dome-shaped washer 124 is slidably mounted on plunger 118 beneath prongs 122. A spring 126 is positioned on the plunger beneath washer 124 and held in place by means of a nut 128 threaded on the lower end of the plunger. Another spring 130 is positioned outside the housing 76 in a position surrounding bushing 120 and plunger 118. This spring is contained between the top surface of the housing and a cap 132 pinned to the upper end of plunger 118 as at 134.

As can be generally seen in FIG. 2, switch 75 is mounted in a fixed position on a bracket 136 extending upwardly from the truck chassis 12. A generally L-shaped operating handle 138 is located over the switch and pivotally connected as at 140 to another fixed structural member 142 of the truck. One end of the handle lies directly over cap 132 on operating plunger 118. The other end of the handle is connected by means of a control cable 144 which extends coextensively with the lifting chains 56 over one of the pulleys 48 on shaft 44. The control cable then descends downwardly around a second pulley 148 on base 50 where it then continues upwardly to be connected by means of a clamp 150 to an operating level 152 pivotally mounted to the control panel as at 154. When the lever 150 is pulled upwardly and seated on the ledge 156 on bracket 158, the control cable 144 is placed in tension thus causing the operating handle 138 to pivot in a counterclockwise direction about point 140. This in turn causes the operating plunger to be depressed to the position shown in FIG. 4. At this point, spring 130 is in compression, spring 126 is expanded and, the plate 94 of armature assembly 112 held downwardly against magnet 114. Under these conditions, the switch is closed and the operating circuits of the truck fully operable.

If it is assumed that during operation of the truck, the operator inadvertently causes the lift forks 74 to become engaged on an adjacent bin or shelf when the carriage assembly is being lowered, the following will occur; as soon as the forks are engaged on the shelf, slack will begin to develop in the lifting chains 56. Since cable 144 extends coextensively with the lifting chains, the tension therein will also immediately begin to lessen. As this occurs, the compressive force of spring 150 will begin to push operating plunger 118 upwardly. However, until the attractive force of magnet 114 is overcome, this upward axial movement of operating plunger 118 will cause spring 126 to be compressed between washer 124 and nut 128. This condition is illustrated in FIG. 5 wherein it can be seen that spring 130 i partially expanded and spring 126 partially compressed, with the plate 94 of armature assembly 112 still held downwardly against magnet 114. At this point, some slack has developed in in the lifting chains 56 and cable 144, but not enough to create a danger of the lifting chains jumping their respective sheaves. By this time, an alert operator would have become aware of the fact that the lifting forks 74 were engaged on the shelf and as a result would have reversed the movement of piston rod 38 to raise the carriage assembly from its engaged position.

However, should the operator fail to act with suflicient rapidity, further expansion of spring 130 as slack continues to develop in cable 144 will continue to move operating plunger 118 upwardly under the influence of spring 130, thus causing the smaller spring 126 to be further compressed. When the compressive force of spring 126 finally overcomes .the attractive force of magnet 114, the plate 94 of armature assembly 112 will be sprung upwardly and the switch opened as indicated in FIG. 6. By properly selecting the size and strength of the springs 130 and 126, the switch can be made to open prior to the development of a dangerous degree of slack in the lifting chains. As soon as the switch opens, the main power supply of the truck is isolated and all components brought to a halt. This gives the operator time to analyze the situation and once he had done so, he may reactivate the apparatus by simply pulling on the control cable to create tension therein. When this is done, the operating handle 138 is again pivoted in a counterclockwise direction about point 140, resulting in the compression of spring as the operating plunger 118 is depressed. This will in turn allow the plate 84 of armature assembly 112 to gradually drop until it is forced downwardly into the enclosed position shown in FIG. 4 by the attractive force of the magnet 114.

By providing a delayed action switch of the abovedescribed type, a substantial advantage is gained in that a tolerable amount of slack is permitted to develop in the lifting chains and various control cables before the switch is sprung open to interrupt the main power supply of the truck. In this manner, the operator if alert may correct the conditions causing slack in the cables without having to manually reset the switch.

It is our intention to cover all changes and modifications of the embodiment herein chosen for purposes of disclosure which do not depart from the spirit and scope of the invention.

We claim:

1. A delay action electrical switch comprising: spaced electrically insulated contacts; an electrically conductive armature movable between a normally closed position abutting said contacts to an open position spaced therefrom; magnetic holding means positioned adjacent said armature, said holding means being operative to exert an attractive closing force which urges said armature into the closed position; a plunger axially movable through an opening in said armature; spring means carried by said plunger in a manner such that axial movement of said plunger relative to said armature in a direction opposite to the attractive closing force of said holding means will cause said spring means to exert an opening force on said armature, which opening force will gradually increase to a point at which it exceeds the attractive closing force of said magnetic holding means, at which point the said armature will be moved under the influence of said opening force to the open position.

2. The apparatus as claimed in claim 1 wherein said armature is pivotally mounted for movement between said open and closed positions.

3. The apparatus as claimed in claim 2 wherein said spring means is comprised of a coiled spring axially mounted on said plunger, said coiled spring being constrained axially between a fixed member on said plunger and said armature when said plunger is axially moved in a direction opposite to the attractive closing force of said holding means.

References Cited UNITED STATES PATENTS 2,853,627 9/1958 Karl 200-161 2,900,474 8/1959 Welsh 200-113 3,224,529 12/1965 Gandolfo l879 BERNARD A. GILHEANY, Primary Examiner. H. BROOME, Assistant Examiner.

US. Cl. X.R. 200161 

